The LEV-type framework is characterized by heptadecahedral cavities to which the LEV-type zeolites owe their large micropore volume, although this structure only has small eight-membered ring (8MR) pore openings. The framework density of Levyne is comparable to those of Chabazite (CHA) and Erionite (ERI) having closely related framework structures. Thus, although recent research efforts have focused on large or ultra-large pore zeolites having twelve MR or larger pore openings, small pore zeolites are still of importance because they exhibit zeolite-specific definite shape selectivity with respect to reactant molecules in catalyst applications. In particular, such small pore zeolites having large micropore volumes are attractive due to their large adsorption capacities.
Synthetic Levyne-type zeolites are typically prepared using exotic organotemplates as structure directing agents, such as quinuclidine-based templates, such that their synthesis typically involves high costs. A lower cost alternative is to use diethyldimethylammonium hydroxide as a structure directing agent wherein the diethyldimethylammonium cations act as the organotemplate. Thus, U.S. Pat. No. 7,264,789 B1 discloses a method for preparing LEV-type zeolites which alternatively uses choline and diethyldimethylammonium as organotemplate. A method for the preparation of the LEV-type zeolite RUB-50 using the diethyldimethylammonium cation as oraganotemplate is disclosed in Yamamoto et al. Micropor. Mesopor. Mater. 2010, Vol. 128, pp. 150-157.
Nevertheless, although some progress has been achieved regarding the costs of the organotemplate used in the synthesis of LEV-type zeolites, there remains a need for further improving the efficiency of the synthetic procedure which normally further involves both calcination and ion-exchange steps for obtaining the H-form of the aforementioned LEV-type zeoites. In particular, in addition to requiring the removal of the organotemplates used in synthesis by thermal treatment of the crystallization products in a calcination step, the product must furthermore be subject to an ion-exchange procedure for removing alkali metal ions, and in particular sodium or potassium present as counter-ions to the negatively charged framework structure in the zeolitic material for finally obtaining the commercially interesting H-form of the LEV-type zeolites. Said ion-exchange to the H-form is normally achieved by subjecting the calcined material to one or more ion-exchange steps with an ammonium salt, after which ammonia is removed by thermal treatment of the ion-exchanged product to finally obtain the H-form LEV-type zeolite.
Furthermore, the synthetic procedures of LEV-type zeolites typically afford nanocrystalline materials which require a relatively elaborate work-up procedure for their washing and isolation. Thus the washing and isolation procedures disclosed in Yamamoto et al. as well as in U.S. Pat. No. 7,264,789 B1 both involve centrifugation procedures coupled to intermediate washing steps for obtaining the crystallized material in a form in which it may then be further processed. In particular, the isolation methods of the nanocrystalline products require an exceptional handling using costly apparatus. More importantly, however, said requirements constitute an important obstacle to the production of LEV-type zeolites on an industrial scale due to the considerable difficulties of efficiently working up such materials in a large scale synthetic environment.
Consequently, in view of the above, it is apparent that the production LEV-type zeolitic materials remains a laborious enterprise which involves a time- and cost-intensive work-up, such that there remains a considerable need of providing an efficient procedure for their production. This applies in particular with respect to the prospect of efficiently producing LEV-type zeolitic materials on an industrial scale.